Integrated circuit packages are formed using a variety of techniques. Heat sinks are often used in integrated circuit packages to dissipate heat from the device, preventing any failure of or damage to the device. Heat sinks are made of a variety of heat conducting materials and are formed in a variety of shapes to adequately conduct the heat from the device. One application of a heat sink is the use of a lid, where the lid is attached to the backside of the die of an integrated circuit to reduce the heat of the die and enable the integrated circuit to function properly. That is, the lid helps to dissipate heat to keep a semiconductor junction, such as a junction of the transistor, below a maximum specified operating temperature. Another purpose of the lid may be to provide some physical protection for the components within the lid. A lid for an integrated circuit, commonly made of a metallic or ceramic material, is attached on top of a flip chip package to provide protection to the silicon die and other discrete surface mount components.
However, these types of lid heat sinks often exhibit the problem of separating from the top of an integrated circuit package. Because the adhesion strength of any adhesive used to attach the conductive lid may not be strong enough to hold the conductive lid to the package, the conductive lid may come off of the package. Proper material construction and processing of the lid, the package, and the adhesive is required so that the lid will stay attached to the package during the assembly and long term field usage. Degradation of the adhesion may be caused by many factors, including improper dispensing of an adhesive which will not produce a complete adhesive surface as designed, shear stresses induced as a result of thermal expansion/shrinkage differences at the interfaces, push/pull stresses induced due to warping of the silicon, package, and/or board, adhesive degradation due to chemical attack, etc. Excessive component handling stresses, such as excessive torque or pressure during test, assembly, or rework, may also result in separation of the lid from the package.
In a conventional Flip Chip Ball Grid Array (FCBGA) package with a lid, the lid is attached to the backside of the die using an adhesive Thermal Interface Material (TIM) layer, also known as lid attach material. The lid is also coupled to the substrate using a lid seal adhesive where the lid itself encapsulates the die. The TIM layer is thermally conductive and it provides a good thermal path for heat to flow from the back of the die to lid. Usually the TIM layer is filled with thermally conductive fillers such as silver powder, gold powder or alumina. Heat dissipation from die backside of the die is affected by the type of TIM material, the total thickness of TIM layer, and the convection speed.
In case of a molded flip chip package, the lid is applied directly to the die, and the die is underfilled as well as overmolded with a mold compound, resulting in the use of a mold compound to encapsulate the die. An overmolded package offers high reliability, good resistance again harsh environment, and also improves electrical performance because thin core substrates may be used. While a molded flip chip package may employ a lid, one drawback of a conventional molded integrated circuit package is the inferior heat dissipation from backside of the die. Since mold compound between the die and the lid is composed of epoxy matrix and silica fillers, its heat conductivity is poor compared to a TIM layer. Moreover, due to differences in package and die tolerances, the mold cap or bondline thickness may vary and degrade the heat dissipation rate. The heat dissipation from the backside of the die, is significantly lower than the standard FCBGA structure.
Accordingly, there is a need for an improved molded integrated circuit package and method of forming a molded integrated circuit package.